1. Field of the Invention
The present invention relates generally to wireless mobile telecommunication networks and, more specifically, to establishing a new mobile-originated call after a previous failure to establish a call.
2. Description of the Related Art
In wireless mobile, i.e., cellular, telecommunications, there are times when a mobile station attempts to make a call in an area of poor coverage but the call fails to be established. The term “coverage” refers to continuity in quality and strength of the air interface (radio) signals across a geographic area. In an area of “good coverage,” the signals communicated between a mobile station and a base station are generally sufficient in quality, strength or other relevant parameters to enable calls to be made and received at the mobile station throughout the area. In an area of little or no coverage, the signals communicated between a mobile station and a base station, if any can be received at all, are of too poor a quality or otherwise not sufficiently “good” to enable calls to be made and received at the mobile station. In still other areas there may be poor or spotty coverage. Such areas are most often at the boundaries between adjacent cells or otherwise at edges of good coverage areas but also occur where buildings or natural features prevent good signal propagation. Sometimes, as a mobile station moves from one location to another, coverage improves or worsens. If a mobile station user dials a number but the call fails, the user will typically redial and try again. The call often can be established on such a second try, especially if the user is moving into an area of better coverage.
When a mobile station user attempts to make a call, but the air interface signal communication is too poor for the network to establish the call, i.e., the call fails, the mobile station may search for a base station with which signal communication is good. (Although the generic term “base station” is used herein for purposes of clarity, the equipment is commonly referred as a “Base Transceiver Station”/“Base Station Controller” in the lexicon of networks conforming to the Global System for Mobile telecommunications (GSM) standard, a “Node-B”/“Radio Network Controller” in the lexicon of networks confirming to the Universal Mobile Telecommunications System (UMTS) standard, or by other names in other types of networks.) If the mobile station finds such a base station, the base station may be one other than that which was previously involved in the failed call, even if the user has not moved, as the coverage areas of adjacent base stations generally overlap to some extent. Thus, if a user immediately redials the number after a failed call, the call may be successfully established on the second attempt if the mobile station has found a better base station with which to communicate. When a mobile station initially establishes communication with a base station, a process known as registration occurs, whereby the mobile station makes its presence and ability to communicate through that selected base station known to the network. The network element that maintains such registration information is known as the Home Location Register (HLR). If such a mobile station is roaming, similar information noting the location of the visiting mobile station and its ability to communicate through a selected base station is recorded in a Visitor Location Register (VLR), which is in many instances combined with the HLR as a single unit of network equipment.
It is known for some mobile stations to automatically (i.e., without user input) redial or re-try a call to the same number following call failure. Such mobile stations do not necessarily perform any actions other than redialing in response to a call failure.
As discussed above, areas of poor coverage commonly occur at the edges of network coverage. Service providers adding newer third-generation (3G) network equipment to supplement (and eventually supplant) existing second-generation (2G) equipment in the same coverage areas can give rise to new coverage edges. Until a service provider has completely substituted 3G network equipment (e.g., Universal Mobile Telecommunications System or UMTS), for its existing 2G network equipment (e.g., GSM), a service provider's 2G network portions will continue to provide greater coverage than its UMTS or other 3G network portions, thereby creating difficulties for users. For example, a dual-mode mobile station at the edge of an area having UMTS service may fail to establish a call in UTMS mode, but may be able to establish a call in (2G) GSM mode. Accordingly, in response to the call failure, the mobile station may search for a better base station with which to communicate, and it may find and register with a base station of the GSM network portion rather than the UMTS network portion due to the greater coverage of the GSM network portions. However, the user cannot obtain the benefit of the mobile station having found and registered with a better base station (whether of the 3G or 2G network portion) unless the user redials and tries again. A user generally must press a “Talk” or similar button on the keypad to redial. The user has no way of knowing whether the mobile station has registered with a better base station unless the user tries to make another call. Thus, a user will often press the button to redial after a call failure in hope that re-trying the call will result in call establishment. If the mobile station has found and registered with a better base station at that time, the redial may result in call establishment. If the mobile station has not found such a base station, the redial may result in yet another call failure. A user may repeatedly redial in this manner if multiple attempts fail to establish the call. Having to redial after a call failure can be especially perplexing and thus annoying to users operating in areas that they have come to believe are well covered by their service provider's network but which, in reality, are only well covered by the 2G portions of their service provider's network.
It would be desirable to relieve a user from having to initiate or re-initiate a call to determine whether a call is likely to be more successful than a previous call. It is to such a method and system that the present invention is primarily directed.